Appliance theft control alarm system



Oct 1970 v. B. coN s 3,537, "71

APPLIANCE THEFT CONTROL ALARM SYSTEM Filed March 20, 1968 INVENTOR VANB. CON ES ATTORNEYS 3,537,095 APPLIANCE THEFT CONTROL ALARM SYSTEM VanB. Cones, Indianapolis, Ind., assignor, by mesne assignments, to ConesJet Air System, Inc., Indianapolis, Ind., a corporation of Indiana FiledMar. 20, 1968, Ser. No. 714,715 Int. Cl. G08b 21/00 U.S. Cl. 340-280 8Claims ABSTRACT OF THE DISCLOSURE A11 alarm system particularly suitablefor indicating when an electrical appliance is disconnected from itsgrounded electrical power source, the alarm system comprising firstcircuit means adapted to be connected in parallel with such a source tothe grounded side of such an appliance so that, when the appliance isdisconnected from its source, the first circuit means will bedisconnected from ground. The alarm system further comprises capacitancecoupling means adapted to be connected between the first circuit meansand an electrical power source, output means arranged to alertpersonnel, normally non-conducting electronic switch means arranged tocontrol the flow of current through the output means, the switch meanscomprising a control electrode, and second circuit means for connectingthe control electrode to the junction between the capacitance couplingmeans and the first circuit means so that, when the first circuit meansis disconnected from ground, the voltage coupled through the capacitancemeans is applied to the control electrode to render the switch meansconductive, thereby to energize the output means. Preferably, the secondcircuit means comprises resistance means connected between the controlelectrode and the capacitance coupling means, a unidirectionalconductive device connected between ground and the junction of theresistance means and control electrode, and second capacitance meansbeing chargeable to a voltage level sufficient to render the switchmeans conductive. Also, preferably, the output means is a relay,solenoid or the like arranged to be energized by current flow from adirect current power source and the switch means is of the typecomprising an anode electrode connected to the output means and acathode electrode connected to ground, the junctions between the anodeand cathode being biased so that, when the switch means is renderedconductive by a positive voltage applied to the control electrode, theswitch means will remain conductive as long as a positive voltage isapplied to the anode, thereby to maintain the output means energized.

This invention relates to means for providing an alarm when anelectrical applicance, such as a television receiver, is disconnectedfrom its power source and more particularly for indicating an alarm whensuch an appliance has been disconnected from its conventional electricalpower source receptacle, one side of which is grounded. It will beperceived that the system of this invention is ideally suited for use inthe prevention of theft of appliances. The system is not limited,however, to the prevention or indication of a theft but may be used tosound an alarm when any conductor is, for any reason, disconnected fromground.

It is well known to use relays to warn when appliances have beendisconnected from electrical outlets. Such relays normally compriseswitches arranged to energize an auxiliary alarm circuit, spring meansfor urging the switches to their normally-closed position and anarmature connected to the switches and arranged so that, when the relayis energized, the switches are held open in opposition to the urging ofthe spring means. Thus, if

United States Patent M 3,537,095 Patented Get. 27, 1970 the relay isenergized through the same power circuit as an appliance and theappliance is disconnected, the auxiliary alarm circuit is energized.Relay systems of this type are bulky, expensive, difficult to maintainand inefficient because they consume significant quantities ofelectrical power. Hundreds of such relays installed in alarm systems forlarge hotels and motels would consume thousands of watts of powercontinually and develop a corresponding amount of heat. Further, theinductance or inductive reactance of such a large number of relays wouldtend to decrease the power factor of the electrical load and, whencombined with other inductances, could decrease the power factor to thepoint where the motel or hotel would be charged a higher rate for itselectrical power.

Relay contacts corode with age and the laminations about which theircoils are wrapped may become noisy and chatter. Salt atmosphere, such asmay be encountered in a hotel or motel along the coast, can speed thecorrosion of relay contacts. The maintenance of systems comprising alarge number of relays is a headache to some business operations becausemaintenance personnel are difiicult to find. The replacement of a relayusually requires the changing of one or more mounting screws andunsoldering and soldering at least four wires and perhaps more.

It is a primary object of my invention, therefore, to provide an alarmcomprising means for sensing when a conductor is disconnected fromground, which sensing means does not utilize significant amounts ofelectrical power. My preferred sensing means comprises a normallynon-conducting electronic switch having a control electrode, firstcircuit means connected to the grounded side of an appliance, couplingmeans adapted to be connected between an electrical power source and thefirst circuit means and through the first circuit means to ground andsecond circuit means connected between the control electrode and thejunction between the coupling means and the first circuit means so thatwhen the first circuit means is disconnected from ground, the voltagecoupled through the coupling means is applied to the control electrodeto render the switch means conductive. I have connected the switch meansin series with an output means and a power source so that, when theswitch means is conduct ing, the output means will be energized. Theoutput means may take any number of forms. I prefer to use a relay asthe output means, the relay being arranged to energize an audio-alarmand a visual indicating means.

My preferred first circuit means includes a pair of separable contactsdisposed in a conventional polarized receptacle, one of the contactsbeing connected to a wire which extends through the conventional powercord for an appliance to be connected internally of the appliance to thegrounded side of its power source. Thus, if the power cord is cut or ifthe plug is removed from the receptacle, the first circuit means will bedisconnected from ground and the voltage coupled through the couplingmeans will be available to be applied to the control electrode of theswitch means.

It is another object of my invention to provide such an alarm systemwhich will not utilize significant amounts of electrical power unlessand until an appliance being monitored is disconnected from itselectrical power source.

Another object of my invention is to provide such an alarm systemcomprising an electronic switch for energing an output means, theelectronic switch being arranged so that once it is rendered conductiveby the application of an input signal, it will remain conductive tomaintain the output means energized.

Still another object of my invention is to provide an ultra-low-powerconsuming theft alarm system comprising a minimum number of parts andarranged to give years of a maintenance-free service. I have built andused my system to keep the television sets in thirty motel rooms undersurveillance and the system requires less than two and one-half watts ofelectrical power. Most of this power is required for asemiconductor-type direct current power supply which I prefer to use,and I believe that such a power supply is a sufficient direct currentpower source for use with an alarm system arranged to providesurveillance for a thousand or more different television sets or othersuch appliances.

Still a further object of my invention is to provide such a system whichwill continue to provide an alarm when a power plug has been removedfrom an electrical outlet and a jumper plug has been installed in itsplace. My system is so sensitive that it will provide an alarm when anappliance being monitored is disconnected for a fraction of a second,but will not, for reasons to be discussed hereinafter, give a falsealarm because of power line or other electrical transient voltages.

Other objects and features of my invention will become apparent as thisdescription progresses.

To the accomplishment of the above and related objects, my invention maybe embodied in the form illustrated in the accompanying drawing,attention being called to the fact, however, that the drawing isillustrative only, and that change may be made in the specificconstruction illustrated and described, so long as the scope of theappended claims is not violated.

The sole drawing accompanying this specification is a schematic diagramof a preferred embodiment of my system,

Referring to the drawing, it will be seen that I have illustrated atelevision receiver, indicated generally by the reference numeral 14, athree-conductor power cord 15, a polarized electric power plug 16 on oneend of the power cord and a polarized power source receptacle 17 intowhich the plug 16 is inserted. Two of the conductors of the power cordare connected to the television receiver 14 as indicated at 15', 15".The third wire, indicated by the reference numeral 34, of the power cord15 is connected to the ground wire 30 of the power cord as indicated at33. The said ground wire is connected through the plug 16 to a contactmember in the receptacle 17, the contact member 25 being connected toground. The wire 34 is connected through the plug 16 to a contact member24 in the receptacle.

It will be understood that the three wires of the power cord 15 areconnected to male contact members in the plug 16 and that the receptacle17 includes three female contact members for receiving, respectively,the contact members carried by the plug 16. Thus, the reference numeral24 represents a male contact member and a female contact member forseparably connecting the wire 34 to the wire indicated by the referencenumeral 32.

The connecion indicated at 33 is preferably made within the housing ofthe television receiver 14 and may, if desired, be made directly to theconnection indicated by the reference numeral 15.

With the above-described arrangement, the wire 32 will be disconnectedfrom ground if the power cord 15 is cut or severed to break either theground wire or the wire 34 or if the plug 16 is pulled away from thereceptacle 17.

I have illustrated a plurality of contact members 24, each of which isconnected to the end of a wire 32'. It will be understood that thesecontact members 24 are provided so that other appliances, such as othertelevision receivers, can be monitored. For example, a receptacle 17having a contact member 24 can be placed in each of rooms in a motel foruse with television receivers equipped with power cords similar to thepower cord 15.

My illustrated alarm system is arranged to provide surveillance of fourdifferent electrical appliances. It will be understood, however, thatany number of appliances can be monitored merely by expanding my basicsystem, I have found that it is more convenient to arrange my system toprovide surveillance for groups of 4 appliances and to provide an alarmindicating in which group an appliance has been tampered with as well asthe particular appliance. This arrangement will be discussed more fullyhereinafter.

The wires 32 and 34 and the contact members connecting these wires,which contact members are indicated by the reference numeral 24,comprise the above-mentioned first circuit means which is disconnectedfrom ground when the plug 16 is removed from the receptacle 17 or whenthe wire 34 or the wire 30 is severed.

I prefer to mount the components of my system on a panel 19 which ismetal and, therefore, electrically conductive. It will be understood,however, that this feature is not critical, but is merely a matter ofconvenience.

I have illustrated another three-conductor power cord 19', one end ofwhich is connected to another conventional polarized plug 20 which isadapted to be plugged into another conventional polarized receptacle20'. Two of the female contact members 36, 37 in the receptacle 20 areconnected to ground as illustrated.

The panel 19 is maintained at ground potential by the wire 38 of thepower cord 19, the wire 38 being connected between the panel 19 asindicated at 57 and the male contact member in the plug 20 which isreceived in the female contact member 36. The other ground terminal 37is connected through the power cord 19' to the following groundterminals 49, 43, and 41. The power cord 19' includes the conventionalhigh-voltage conductor wire 28 which is connected through a switch 21 tothe illustrated terminal 48.

The power sources represented by the receptacles 17 and 20 arepreferably conventional alternating current power sources. Thus, analternating current potential is coupled from the terminal 48 throughthe illustrated wire 26 to the illustrated terminal 48. A capacitor 1 isconnected between one of the terminals 48' and the end of the wire 32 atthe illustrated terminal 31. Thus, the alternating current voltage atthe terminal 48 is coupled through the capacitor 1, terminal 3-1, wire32, wire 34 and the wire 30 to ground. In a similar manner, a capacitor1' is connected between each of the other terminals 48' and one of thewires 32 to provide an alternating current voltage at each of theillustrated contact members 24'.

I prefer to connect a neon lamp 2 between each junction 31, i.e., thejunction between each capacitor 1 and wire 32, and ground. In theillustrative system, the neon lamps 2, 2' are connected between theterminals 31, 31' and the ground terminal 41. These lamps 2, 2' will notbe energized as long as the wires 32, 32' to which they are respectivelyconnected are connected to ground. The lamp 2 will not be energized, forexample, as long as the plug 16 is in the receptacle 17 and the wires30, 34 have not been cut or disconnected at the point 33.

If, for some reason, the plug 16 is removed from the receptacle or, ifone of the wires 30, 34 is cut, the alternating current voltage coupledthrough the capacitor 1 to the terminal 31 will be ungrounded and,therefore, the lamp 2 will be energized. This lamp 2 will then serve asa visual indication that the television receiver 14 has beendisconnected from its power source.

The ungrounded alternating current voltage at the terminal 31 is alsoavailable, when properly rectified, to trigger an electronic switchingmeans such as the illustrated silicon controlled rectifier 6. Thus, Ihave connected each terminal 31, 31 to a terminal indicated at 39through an isolation resistor 3, 3'. These isolation resistors 3, 3'serve to reduce the potential of the alternating current voltage at theterminals 39 to a value which is suitable for use in triggering asilicon controlled rectifier.

The terminal 39 is connected by a wire 51 to the control electrode,commonly called the gate electrode of the silicon controlled rectifier6. In order to provide a positive voltage only to the gate electrode, Ihave connected a diode 4 between the terminal 39 and the ground terminal41, the cathode of the diode 4- being connected to the terminal 39. Inorder to apply the proper voltage level to the gate electrode, I haveconnected a capacitor in parallel with the diode 4. The chargingrequirement of this capacitor 5 is sufiicient to prevent power linevoltage transients, load switching transients and other voltagedisturbances from triggering the silicon controlled rectifier 6 to givea false alarm, but small enough to permit the silicon controlledrectifier 6 to be triggered by the disconnection of the televisionreceiver 14, or any other appliance .being monitored, from its powersource, even if it is only disconnected for a fraction of a second.

Each resistor 3, 3 and the diode 4 and capacitor 5 comprise theabove-referred to second circuit means for connecting the controlelectrode of the silicon controlled rectifier to the junction betweenthe capacitor 1 and the above-referred to first circuit means.

The silicon controlled rectifier 6 may be used to energize or, morespecifically, to control the energization of any suitable output meanssuch as an alarm bell or buzber, a warning light or any other suitablemeans for alerting personnel.

'In the illustrative embodiment, the anode and cathode electrodes, i.e.,the input and output electrodes, of the silicon controlled rectifier 6are connected in series with the coil of a relay 7 so that, when thesilicon controlled rectifier is triggered to its conductive state,current can flow through the coil to actuate the armature of the relay.The armature of the relay 7 is connected by a linkage 7' to a pair ofswitches 46, 47. The switch 46 is arranged so that, when the relay 7 isenergized, a neon lamp 8 is energized by current flow from the terminal48 through wire 56 and the lamp to the ground terminal 41. The lamp 8,when energized, will alert personnel to the fact that one of the wires32, 32' has been disconnected, at least, momentarily, from ground. Thatis, the lamp 8 will provide a visual indication that one of theillustrated group of monitoring circuits, i.e., one of the wires 32, 32,has been disconnected from ground.

I prefer to use a latching-type silicon controlled rectifier 6, i.e., arectifier which will remain conductive once a proper triggering voltageis applied to the gate electrode and as long as there is a propervoltage applied to its anode electrode. Such silicon controlledrectifiers are well known and commercially available and need not bediscussed, in detail, in this description.

I also prefer to use a direct current power source, indicated by thereference numeral 13, the positive voltage output of which is connectedto a terminal 42 and through the terminal 42 and the coil of the relay 7to the anode of the silicon controlled rectifier 6. The negative side ofthe output of the power supply 13 is connected to the ground terminal43. In the illustrative embodiment, the direct current power source 13is arranged to convert the alternating current voltage between theterminal 48 and the ground terminal 49 to a direct current voltage. Itwill be understood, however, that this is merely a matter of convenienceand that, for instance, a battery may be arranged to provide current forenergizing the relay 7.

When the switch 21 is closed, a positive voltage is available at theanode of the silicon controlled rectifier 6. Thus, when the siliconcontrolled rectifier 6 is triggered to its conductive state, current canflow through the coil of the relay 7 through silicon controlledrectifier 6 and wire 50 to the ground terminal 41 and the current willcontinue to flow until the switch 21 is opened. This continued currentflow through the coil of the relay 7 will maintain the switch 46 closedto maintain the lamp 8 energized.

Further, I prefer to provide an audio alarm, such as the illustratedbuzzer 12, which is connected in series with the switch 47 between theterminal 48 and the ground terminal 55. Thus, the buzzer 12 will remainenergized in the same manner that the lamp 8 will remain energized.

I have arranged my system so that, when one of the wires 32, 32 isdisconnected from ground, the lamp 8 and buzzer 12 will remain energizedeven after the wire is reconnected to ground. Thus, if a thief pulls theplug 16 from the receptacle 17 and inserts another plug into thereceptacle 17 to connect the contact member 24 to the contact member 25,lamp 8 and buzzer 12 will remain energized to indicate that thetelevision receiver 14 has been tampered with. Further, the lamp 8 willremain energized even though the lamp 2 is deenergized when the wire 32is reconnected to ground. If the personnel responsible for monitoringthe alarm system happen to miss seeing the particular lamp 2, 2 which isenergized because one of the wires 32, 32 is disconnected from groundand then subsequently reconnected, they will at least be aware that oneof four television receivers has just been tampered with. In the motelenvironment discussed previously, the continued energization of the lamp8 and buzzer 12 will indicate to the necessary personnel that they mustwatch only the four rooms having the receptacles containing the contactmembers 24, 24 and will not have to watch dozens or hundreds of otherrooms to see which television receiver has been tampered with.

I have illustrated a terminal 9 which may be connected to other groupsof capacitors corresponding to the capacitors 1, 1; a terminal 10 whichmay be connected to the coils of other relays corresponding to the relay7; and a terminal 11 which may be connected from other switchescorresponding to switch 47. When my alarm system is used, for instance,to provide surveillance of television receivers in a multitude of motelrooms, each group of wires 32, 32 and their associated capacitors 1, 1is preferably used with a single silicon controlled rectifier 6 andrelay 7 combination. Thus, there will be one silicon controlledrectifier 6 and relay 7 associated with each group of rooms undersurveillance. It may be desirable, however, for some motel or hoteloperations, to use only one silicon controlled rectifier 6 and relay 7for monitoring the power connection to every television receiver or, forthat matter, every appliance in the hotel or motel. In such a case, if athief happens to pull a plug 16 and then inserts another plug to connectthe contact members 24 and 25 of a receptacle, it will be necessary, orat least advisable, to watch every room in the motel or hotel.

The silicon controlled rectifier 6 as used in my system is a normallynon-conducting electronic switch. The relay 7 remains deenergized untilthe switch 6 is rendered conductive. Thus, the only significant powerrequirement of my system is to keep the direct current power supply 13energized. I have found that a conventional semiconductor power supply,which is well known in the electrical and electronic arts and which neednot be discussed, in detail, in this description, will providesulficient power to operate large numbers of relays 7, but will onlydraw 2% watts of power when such relays are deenergized. This 2%. wattsis required to keep the power supply 12 in a state in which, ifrequired, it can provide enough power to operate the relays.

My illustrated system may be reset after a wire 32, 32' has beendisconnected and subsequently reconnected to ground by opening theswitch 21 which deenergizes the power supply 13 to permit the switches46 and 47 to open and then reclosing the switch 21. Further, it will beapparent that a switch (not shown) may be used manually to disconnectthe buzzer 12 from its power source. That is, it is anticipated that,once the necessary personnel has been alerted, the personnel may desireto disconnect the buzzer 12 and to rely on the lamp 8.

I prefer to connect a resistor 60 between the terminal 42 and the coilof the relay 7 and a capacitor 62 between ground and the junctionbetween the relay coil and the resistor 60. The network comprising theresistor 60 and capacitor 62 acts as an inductive filter to preventinductive kicks of some relays 7 from momentarily disturbing othersilicon controlled rectifiers 6 on the panel 19. That is, the resistor60 and capacitor 62 serve to isolate the illustrated relay 7 from powersource 13 transients caused by the energization of other relays whichare connected to the power source.

In the alarm system which I have constructed and tested, the followingcharacteristics were selected for the components:

Capacitor 1-0.01 ,uf., 1000 volts Capacitor 5-0.S ,uf., 200 volts, D.C.Resistor 3-l megohm, /2 watt Resistor 60l00 ohm, 1 watt 1O Capacitor6216 at, 100 volts, D.C.

What is claimed is:

1. An alarm system for indicating when an electrical appliance isdisconnected from its grounded electrical power source, said alarmsystem comprising first circuit means adapted to be connected inparallel with such a source to the grounded side of such an appliance sothat, when such an appliance is disconnected from its source, said firstcircuit means will be disconnected from ground, capacitance meansconnected between said first circuit means and the high side of analternating current electrical power source, said first circuit meansbeing substantially purely conductive between its junction with saidcapacitance means and ground, output means arranged to alert personnel,normally non-conducting electronic switch means arranged to control theflow of current through said output means, said switch means including acontrol electrode, and second circuit means for connecting said controlelectrode to the junction between said capacitance means and said firstcircuit means so that, when said first circuit means is disconnectedfrom ground, the alternating current voltage coupled through saidcapacitance means is applied to said control electrode to render saidswitch means conductive, thereby to energize said output means.

2. An alarm system as in claim 1 wherein said second circuit meanscomprises normally non-conducting resistance means connected betweensaid control electrode and the junction between said capacitance meansand said first circuit means, an unidirectional conductive deviceconnected between ground and the junction of said resistance means andsaid control electrode, and second capacitance means connected betweenthe last mentioned junction and ground, said second capacitance meansbeing chargeable to a voltage level sufficient to render said switchmeans conductive when said first circuit means is disconnected fromground to cause current to flow through said resistance means.

3. In combination, first means for connecting an electrically-operatedappliance to an alternating current electrical power source, one side ofwhich is grounded, said first means including conductor means arrangedto connect one side of such an appliance to the ground side of such anelectrical power source, first circuit means connected to said conductormeans at a point adjacent its connection to such an appliance, wherebysaid first circuit means is connected to ground, capacitance meansconnected between said first circuit means and the high side of such analternating current power source, said first circuit means beingsubstantially purely conductive between its junction with saidcapacitance means and ground, output means arranged, when energized bycurrent flow therethrough, to alert personnel, normally non-conductingelectronic switch means arranged to control the flow of current throughsaid output means, said switch means including a control electrode, andnormally nonconducting second circuit means for connecting said controlelectrode to the junction between said capacitance means and said firstcircuit means so that, when said 70 first circuit means is disconnectedfrom ground, the alternating current voltage coupled through saidcapacitance means is applied through said second circuit means to saidcontrol electrode to render said switch means conductive, thereby toenergize said output means.

4. The combination of claim 3 wherein said second circuit meanscomprises unidirectional conductive means connected between said controlelectrode and ground to establish the polarity of the voltage applied tosaid control electrode and wherein the cathode of said unidirectionalconductive means is connected to said control electrode, and whereinsaid second circuit means further comprises normally non-conductingresistance means connected between said control electrode and thejunction between said first circuit means and said capacitance means andsecond capacitance means connected between said control electrode andground, whereby, when said first circuit means is disconnected fromground, current flows through said resistance means and said secondcapacitance means is charged by such current flow with a positivevoltage with respect to ground and sufiicient to render said switchmeans conductive.

5. Means for providing an alarm when a grounded conductor isdisconnected from ground, said means comprising capacitive alternatingcurrent coupling means connected between the high side of an alternatingcurrent electrical power source and such a conductor, the low side ofsaid power source being connected to ground, output means, switch meansarranged to control the flow of current through said output means, saidswitch means comprising an input electrode, an output electrode and acontrol electrode, said control electrode being responsive to apredetermined electrical potential and eifective, when such a potentialis applied thereto, to render said switch means conductive between saidinput and output electrodes, thereby to energize said output means, andnormally non-conducting circuit means connected between said controlelectrode and the junction between said capacitive coupling means andsuch a conductor, said circuit means being effective, when such aconductor and said junction is disconnected from ground, to apply such apredetermined potential to said control electrode.

6. In combination, a power cord for connecting an electrically-operatedappliance to an alternating current electrical power source, one side ofwhich is grounded, said power cord including a first conductor wirearranged to connect one side of such an appliance to the ground side ofsaid an electrical power source and a second conductor wire connected tosaid first conductor wire at a point adjacent its connection to such anappliance, whereby said second conductor wire is connected to ground, afirst alternating current capacitor connected between said secondconductor wire and the high side of said power source,electrically-operated means for alerting personnel, a relay arranged,when energized by current flow through its coil, to energize saidpersonnel alerting means, a normally non-conducting electronic switchhaving an anode, cathode and control electrode, said electronic switchbeing connected between a first side of said coil and ground, the secondside of said coil being connected to a second direct current powersource so that, when said electronic switch is rendered conductive,current can flow through said coil, a normally non-conducting resistorconnected between said control electrode and the junction between saidfirst capacitor and said second conductor wire, a diode connectedbetween ground and the junction between said resistor and said controlelectrode, a second capacitor connected between the last said junctionand ground, said second capacitor being chargeable to a voltage levelsuflicient to render said electronic switch conductive, whereby, whensaid second conductor Wire is disconnected from ground, the alternatingcurrent voltage supplied by such a first power source and coupledthrough said first capacitor is rectified and applied to said controlelectrode to render said electronic switch conductive, thereby toenergize said relay.

7. An alarm system including a first alternating current capacitorcoupled between the high voltage wire of a commercial power source and awire grounded inside of an appliance, a silicon controlled rectifier, anormally nonconducting first resistor coupled between the grounded ter-9 minal of said first capacitor and the gate electrode of said siliconcontrolled rectifier, a diode and a second capacitor coupled betweensaid gate of said rectifier and ground, an output means, secondresistors, and a direct current source, the anode of said siliconcontrolled rectifier being coupled to said output means which isconnected in series with said second resistor to the positive side ofsaid direct current source, the cathode of said silicon controlledrectifier being coupled to ground.

8. An alarm system for protecting a plurality of appliances againsttheft, including a plurality of first alternating current capacitors,each first capacitor having one terminal coupled to the high voltagewire of a commercial alternating current power source connected to saidappliaces and its other terminal coupled to a wire grounded inside oneof said appliances, a normally non-conducting resistor associated witheach first capacitor, the grounded terminal of each capacitor beingconnected to one side of its associated said resistor, a siliconcontrolled rectifier, the other side of each said resistor beingconnected to the gate of said rectifier, an output means, secondresistor, and a direct current power source, said rectifier having itsanode References Cited UNITED STATES PATENTS 2,668,289 2/1954 Conrad eta1 340280 X 3,210,751 10/ 1965 Shiraishi 340-256 3,271,736 9/1966 Brownet al 340 253 X 3,289,194 11/1966 King 340256 X 3,407,400 10/1968 Lurie340-256 X 3,425,050 1/1969 Tellerman et a1. 340256 X ALVIN H. WARING,Primary Examiner S. F. PARTRIDGE, Assistant Examiner US. Cl.- X.R. 340256 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,537,095 Dated October 27, 1970 Inventofli) Van B. Cones It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 2, line 16, corrode is misspelled; same column, line 65, "energ"should be energiz Column 3, line 69, several different should beinserted after f" Column 4, line 35, "terminal" should be terminalsColumn 5, line 21, "her" should be zer Column 6, line 29, after "motel"insert or hotel Column 9, line 4, "resistors" should be resistor samecolumn, line 14, appliances is misspelled; same column,

line 16, "appliances" should be appliance Signed and sealed this 9th dayof March 1971.

i Attest:

mm I. mm, a,

Ed 5 M, Fletchfll' Jr.

War figmigflioner of Patents Atmsting Officer

